Materials in crude oil, particularly paraffin, tend to build up in pipelines carrying such crude oil. Some of the materials originate in water used in secondary recovery efforts, but materials other than crude oil and gas exist in the crude in its natural state, and over time, the build up of precipitants on the interior surfaces of pipes degrades performance of the flow of fluids through the pipeline.
When crude oil is pumped from the ground and transported through pipelines, a large heavy material separates and comes out of solution. The main component of this residue is high molecular weight paraffin waxes. In some cases the wax represents as much as 90 percent of the deposited residues, and varies according to the origin of the crude oil.
Over the years, pipeline pigs have evolved to remove paraffin and other materials obstructing pipelines, and each step in the evolution of pigs has typically addressed a specifically identified need in the art. One need recognized in the art involves the removal of hard, solid, crystalline deposits within the pipe. In pipelines carrying crude oil, the deposits may originate from components in the crude, or elsewhere. In natural gas lines, the deposits commonly form at junctions of pipelines where dry and wet gas mix together. Typically, these deposits vary substantially in thickness throughout the pipe, so that a pig that can fit through the smallest diameter of the deposits is not particularly effective in removing the deposits, and larger pigs that effectively attack the deposits are likely to become plugged in the pipe.
To attack these hard, tenacious deposits, a known pipeline pig was developed which comprises a drive cup, a flexible coupling trailing behind the drive cup, and a set of one or more disks in which adjustable studs are molded into the disks. During a first pass of the pig through the pipe, a relatively small size disk is used, and the studs are adjusted to a relatively small diameter to run through the pipe, with relatively few studs installed on the disk(s). With subsequent runs of the pig through the pipe, more studs are added, and the studs are gradually adjusted to larger and larger diameters. Then, a larger size disk is installed on the trailing mount, and the process is repeated, adjusting the outside diameter of the studs and installing larger and larger disks, until the pipe is opened to an extent close to the inside diameter of the pipe. Often, this process may take up to one hundred runs of the pig through the pipe. It will be appreciated that the process is slow and labor intensive.
Thus, there remains a need for a pipeline pig that can aggressively attack such deposits. The present invention addresses this need in the art.